Reportedly instructed to be strained (4)
I believe the answer is:
taut
'be strained' is the definition.
(I've seen this in another clue)
'reportedly instructed' is the wordplay.
'reportedly' indicates a 'sounds like' (homophone) clue.
'instructed' becomes 'taught' ('teach' can be a synonym of 'instruct').
'taught' is a homophone of 'TAUT'.
'to' is the link.
(Other definitions for taut that I've seen before include "Stretched tight or disciplined" , "Fully stretched" , "Without slack" , "Tense, stretched tight" , "Tightly drawn" .)